1. Field of the Invention
This invention is directed to a method and apparatus for both cooling a primary air stream to provide cool air to a specific location while simultaneously cooling a heat exchange working fluid such as water and more specifically to a method and apparatus wherein the working fluid is initially cooled by an evaporative cooling and indirect heat exchange process utilizing first and second auxiliary or waste air streams in order to increase the cooling efficiency of the working fluid which is subsequently utilized in a sensible heat exchange coil to cool the primary air stream or a second fluid. In some embodiments, the primary air stream may also be humidified and further cooled by passing the primary air stream from the primary sensible heat exchange coil through a closed loop evaporative cooler which utilizes a secondary recirculating working fluid. Alternatively, the apparatus may be used to precool air entering a mechanical refrigerated air conditioning device. The process of the present invention provides for both an efficient cooling of the primary air stream and/or an efficient cooling of the working fluid.
2. History of the Related
Heat exchange processes which utilize evaporative cooling of both air and liquids have long been known with the use of such systems being particularly advantageous in arid areas of the world. Due to the low humidity in arid regions it is possible to utilize such fluids as water to reduce the temperature of air being directed into an enclosure such as a residence or place of business without large expenditures of energy. As energy conservation becomes more and more important there have been many proposals for advancing the efficiency and operating characteristics of such evaporative cooling systems.
To date, some of the most efficient evaporative cooling systems incorporate both evaporative as well as indirect sensible cooling of the primary air stream utilizing methods and apparatus which allow an initial cooling of the working fluid by passing the working fluid which is being recirculated through a system in heat exchange relationship with a secondary source of air which is to be vented to atmosphere and not supplied to the primary area of use. In this manner, it is possible to initially cool the working fluid to thereby increase the efficiency of heat exchange with the primary air stream and to cool the primary air stream without significantly adding to the moisture content of the primary air. One such indirect/direct evaporative air conditioning system is disclosed in U.S. Pat. No. 3,116,612 to Pennington. In Pennington the primary source of air is directed across an indirect heat exchanger through which a working fluid flows in a closed loop which includes the indirect heat exchanger and an evaporative heat exchanger. The primary air stream is subsequently divided into an exhaust stream and an end-use stream with the exhaust air stream passing upwardly through the evaporative cooler to thereby evaporatively cool the working fluid prior to the fluid being introduced into the indirect heat exchanger. The second portion of the primary air stream which is directed to the area of end-use, after passing in heat exchange relationship with the indirect heat exchange coils, passes through a second closed loop evaporative heat exchanger wherein the primary air stream is further cooled.
An improvement over the evaporative heat exchange system disclosed in the patent to Pennington is discussed in U.S. Pat. No. 4,926,656 to Hickley et al. This patent discloses an evaporative indirect/direct cooling system and apparatus wherein the working fluid is cooled in a evaporative cooling pack to obtain a temperature well below the wet bulb temperature of a secondary air stream that is supplied to the evaporative cooler. This secondary air is exhausted as waste air with the working fluid being directed to an intermediate evaporative heat exchanger wherein an intermediate air stream is contacted with the working fluid. The working fluid is thereafter introduced into an evaporative heat exchanger wherein the primary air stream is introduced after passing through an indirect cooling coil through which the cooled working fluid passing through each of the evaporative heat exchangers is circulated so that the primary air supply first passes in indirect heat exchange relationship with the working fluid and thereafter into evaporative heat exchange with the same working fluid before being introduced into the space to be cooled. The precooling of the working fluid by use of the intermediate air stream and the first exhaust air stream assists later in the cooling cycle to obtain a desired reduced working fluid temperature whereas the precooling of the primary air stream by indirect heat exchange through a cooling coil through which the working fluid is conducted reduces the temperature of the primary air stream prior to its passing into evaporative heat exchange with the working fluid and thus reduces the moisture content of the ambient air being introduced into the area to be cooled. Although the air cooling system disclosed in the patent to Hickley exhibits increased cooling efficiencies over conventional indirect/direct evaporative coolers further efforts are being made to obtain greater efficiencies in such systems.
Some additional examples of prior art include U.S. Pat. Nos. 4,380,910 to Hood et al., 2,211,886 to Dudley and 3,905,205 to Zusmanovich.